Mufflers are well known to be used with engines in order to quiet the noise generated by the operation of engines. One type of muffling or sound reduction technique sometimes used is based on absorptive techniques. With absorptive muffling, the energy represented by the sound waves dissipates as heat. Generally, it results from passing or directing the sound waves over or through a packing, such as a fibrous packing. The packing absorbs and dissipates the energy of the sound waves by the sound energy being converted into motion of the fibers. Fiber density is an important factor to sound absorbing efficiency. Thus, it is important to provide consistent and controllable fiber density.
Another type of muffling technique sometimes used is shell damping. Sometimes the outer shell of the muffler vibrates and results in unwanted transmission of exhaust noise into the environment. Shell damping reduces the tendency of the muffler shell to vibrate as a result of the sound pressures within the muffler. Effective damping techniques include using fiberglass wraps and fibrous packing.
As can be seen, the use of packing material and fiber wraps in mufflers can lead to desirable muffler performance. Further, fiber wraps or packing material in mufflers can be useful for heat insulation purposes. Improved techniques for constructing mufflers that have such fiber wraps or packing are desirable.